The invention relates generally to sensors and, more particularly, to a sensor assembly that is configured to provide an accurate measurement of a sensed parameter in a high temperature environment.
Various types of sensors have been used to measure the distance between objects. In addition, such sensors have been used in various applications. For example, in turbine systems, the clearance between a static shroud and turbine blades is greatest when the turbine is cold, and gradually decreases as the turbine heats up and as it spins up to speed. It is desirable that a gap or clearance between the turbine blades and the shroud be maintained for safe and effective operation of the turbine. A sensor may be disposed within the turbine to measure the distance between the turbine blades and the shroud. The distance may be used to direct movement of the shroud to maintain the desired displacement between the shroud and the turbine blades.
In certain applications, capacitance probes are employed to measure the distance between two objects. Typically, when such capacitance probes are placed in high temperature environments, the signal processing unit is required to be located in an ambient environment at a distance from the probe. Further, the capacitance probe is connected to the signal processing unit with a cable. The cable adds an impedance component to the sensing circuit and such impedance component depends upon factors such as cable length, geometry and position. The variation in the properties of the cable may produce substantially large noise components in the signal thereby reducing the sensitivity and accuracy of the probes. The long cable itself acts as a means for electromagnetic noise to couple onto the cable reducing the fidelity of measured signal. In certain systems, electronic signal conditioning is employed to compensate for the signal losses due to such noise components. However, the electronic signal conditioning adds complexity and cost to the system design.
Accordingly, there is a need to provide a sensor that would provide a signal with substantially high signal-to-noise ratio at a remote signal processing unit. It would be also advantageous to provide sensor that provides an accurate measurement of a sensed parameter in high temperature environments.